A-LevelBiologyControl and coordination9700/42 · May/June 2024 · Q815 Marks

[Figure 8.1] is a diagram of a sensory neurone.

(a)(i)Name the type of cell represented by cell A.[1]
(a)(ii)Name a type of cell that forms a synapse with structure B.[1]
(a)(iii)Name the cells that form the myelin sheath.[1]
(b)State and explain the differences in the transmission of impulses between myelinated and unmyelinated neurones.[4]
(c)Opioids are therapeutic drugs that are used to relieve pain. Morphine is an example of an opioid. It affects the functioning of synapses. [Figure 8.2] is a diagram of a cholinergic synapse.
(c)(i)With reference to Fig. 8.2, describe the differences between ion channel A and ion channel B.[2]
(c)(ii)Morphine binds to the opioid receptor in the presynaptic membrane. This stops the ion channel A from opening. Suggest and describe the effects of the binding of morphine to this opioid receptor on the functioning of the cholinergic synapse.[4]
(c)(iii)Morphine also binds to the opioid receptor in the postsynaptic membrane. This results in the opening of ion channel C, allowing potassium ions to diffuse out of the cell. Suggest how this would affect the synapse.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[1] (a)(i) receptor ;
[1] (a)(ii) intermediate neurone ; A relay neurone / motor neurone
[1] (a)(iii) Schwann ;
[4] (b) any four from:
[4] (b) differences
[4] (b) myelinated neurone
[4] (b) 1 faster (impulse transmission) ; ora
[4] (b) explanation
[4] (b) 2 myelin (sheath), insulates (the axon) / prevents movement of ions ;
[4] (b) 3 nodes of Ranvier / gaps with no myelin sheath, have voltage-gated channels or nodes of Ranvier / gaps with no myelin sheath, allow movement of ions ;
[4] (b) 4 depolarisation / action potential, occurs only at nodes of Ranvier / gaps with no myelin sheath ; ora
[4] (b) 5 action potentials jump from node to node / saltatory conduction ; ora
[4] (b) 6 longer local circuits / local circuits occur between nodes ; ora
[2] (c)(i) 1 A voltage-gated and B ligand-gated / not voltage-gated or A opens in response to, depolarisation / arrival of an action potential and B opens in response to binding of, acetylcholine / neurotransmitter ;
[2] (c)(i) 2 A for calcium ions and B for sodium ions ;
[4] (c)(ii) any four from:
[4] (c)(ii) 1 no Ca2+ enter (presynaptic, knob / neurone) ;
[4] (c)(ii) 2 vesicles do not, move towards / fuse with, presynaptic membrane ;
[4] (c)(ii) 3 no, ACh / neurotransmitter, released or no exocytosis of, ACh / neurotransmitter ;
[4] (c)(ii) 4 ACh / neurotransmitter, does not bind to, receptor / ion channel B ;
[4] (c)(ii) 5 Na+ does not enter postsynaptic neurone / ion channel B does not open ;
[4] (c)(ii) 6 postsynaptic membrane not depolarised or no action potential generated or impulse not transmitted ;
[2] (c)(iii) any two from:
[2] (c)(iii) 1 inside more negative (charge) or membrane hyperpolarised / membrane potential decreases / potential difference increases ;
[2] (c)(iii) 2 harder to / cannot, reach threshold ;
[2] (c)(iii) 3 no depolarisation of membrane / harder to depolarise membrane or no / fewer / harder to generate, action potentials / impulses ;